This invention relates generally to long-range, supersonic cruise aircraft, and improvements in the wings of such aircraft.
Supersonic transports (SSTs) have been proposed in the past; however, swept-back wings of such aircraft have introduced inefficiencies, due to high skin friction development resulting from the turbulent boundary layer air flow associated with such highly swept wings. This skin friction drag contributes to undesirably high fuel consumption, and results in concomitant high operating expense and short range. Furthermore, the high sweep and short span of such wings results in very inefficient subsonic flight and poor takeoff and landing performance.
Accordingly, the main obstacle to widespread acceptance of the supersonic transport is its relatively poor range and fuel efficiency, resulting in uncompetitive economics. The basic cause of this uncompetitive performance is the low lift to drag ratio (L/D) of presently used and proposed SSTs, at both supersonic and subsonic speeds.
For more than three decades, the aeronautical community has tried to improve the L/D (lift-to-drag ratio) of long-range, supersonic military and civil aircraft designs. Despite these efforts, the gains have been marginal and far from the 30%-plus improvement in cruise L/D needed to approach the range and operating economics of subsonic transports. All of the aerospace industry-proposed designs are based on modifications of the delta wing (a point-forward triangle). The reason for this choice is that the modified delta wing (and other highly swept forms) has been shown theoretically to have lower supersonic drag, due to lift, than a wing planform with relatively low sweep, and also lower wave drag, due to thickness. In consequence, the delta wing can be thicker, thus reducing structural weight and providing more volume for fuel and equipment.
The delta wing family also has recognized disadvantages; and because it has been the sole candidate for SSTs, these disadvantages are widely assumed to be unavoidable for all SSTs. Two of these disadvantages are the delta wing's high drag, due to lift at subsonic speed, and low maximum lift, even at an uncomfortably high angle of attack. These traits lead to the need for high power and high speed during takeoff and landing, resulting in high noise levels.